In answer to Matthew's question, this has been done in Alexis Sanderson's forthcoming book "Śaivism and Brāhmanism". A handout that outlines the book's thesis is available on
alexissanderson.com.
It's safe to say that the Kāpālikas were beyond the pale (vedabāhyatara) for all orthodox brāhmaṇas, but some authorities (e.g. Aparāditya, as I recall) rejected all initiated Śaivas as outside the Veda (vedabāhya) to the same degree as the Buddhists. It is this (inter alia) that, to my mind, makes the application of the term "Hinduism" impossible in the early medieval period.
best,
CW